1. Field of the Invention
The present invention relates to a motorcycle having a boss portion provided on an upper portion of an engine which is interposed between a pair of right and left hanger portions provided on a body frame in such a manner as to project downwardly therefrom. The boss portion is supported by a through-bolt inserted in the hanger portions and the boss portion. A front end portion of a rear swing arm for rotatably supporting a rear wheel is swingably supported by the engine. Furthermore, a chain transmission means for transmitting power of the engine to the rear wheel is disposed on either the right or left side of the engine. In particular, the present invention relates to an improved engine supporting structure for the motorcycle.
2. Description of Background Art
A motorcycle of the above-described type is known, for example, from Japanese Patent Laid-open No. Hei 10-115226, in which an engine is used to function as a member for reinforcing a body frame.
With respect to the above structure for reinforcing the body frame by means of the engine, if a through-bolt is simply inserted in both hanger portions of the body frame and a boss portion of the engine, the engine cannot be certainly integrated with the body frame because a gap occurs between the boss portion and each of the hanger portions. This depends on the accuracy of the width of the boss portion along the axial line of the through-bolt and the accuracy of a gap between the hanger portions. To solve such a problem as disclosed in Japanese Patent Publication No. Hei 5-33195 and Japanese Patent No. 2587815, there has been proposed a structure for integrating an engine with a body frame, characterized in that one of the hanger portions has an insertion hole in which an enlarged diameter head on one end side of a through-bolt is to be inserted, and a slit portion which is continuous to the inner surface of the insertion-hole and which is opened downwardly, wherein after the axial position of the through-bolt relative to the boss portion is adjusted by bringing the enlarged diameter head into direct-contact with the boss portion or interposing a spacer between the boss portion and the enlarged diameter portion, the diameter of the insertion-hole is reduced by narrowing the width of the slit portion, to thereby clamp the enlarged diameter head of the through-bolt in one hanger portion, whereby the engine is integrated with the body frame.
In a motorcycle of a type in which power of an engine is transmitted to a rear wheel via a chain transmission means, a vertical load applied from the engine to hanger portions of a body frame on the side on which the chain transmission means is disposed is larger than a vertical load applied from the engine to the hanger portions on the side opposed to the side on which the chain transmission means is disposed with respect to the engine. Accordingly, if the hanger portion having the above-described slit portion is disposed on the side on which the chain transmission means is disposed, the supporting strength of the engine may be affected by the disposition of the chain transmission means.
In view of the foregoing, the present invention has been made, and an object of the present invention is to provide an engine supporting structure for a motorcycle, which is capable of integrating an engine with a body frame so as to make the engine effectively function as a member for reinforcing the body frame, while preventing the supporting structure of the engine from being affected by disposition of a chain transmission means.
To achieve the above object, according to the present invention, there is provided an engine supporting structure for a motorcycle including: a boss portion provided on an upper portion of an engine is interposed between a pair of right and left hanger portions provided on a body frame in such a manner as to project downwardly therefrom and is supported by a through-bolt inserted in the hanger portions and the boss portion; a front end portion of a rear swing arm for rotatably supporting a rear wheel is swingably supported by the engine; and a chain transmission means for transmitting a power of the engine to the rear wheel is disposed on either the right or left side of the engine; the engine supporting structure being characterized in that one hanger portion located on the side opposed to the side on which the chain transmission means is disposed with respect to a vehicular center line has an insertion hole in which an enlarged diameter head on one end side of the through-bolt is to be inserted, and a slit portion which is continuous to the inner surface of the insertion hole and which is opened downwardly; and a fastening bolt is screwed in the one hanger portion for narrowing the slit portion to reduce the diameter of the insertion hole after the through-bolt is inserted in the hanger portions and the boss portion in a state in which the axial position of the through-bolt relative to the boss portion is adjusted.
With this configuration, one of the hanger portions has the insertion hole in which the enlarged diameter portion of the through-bolt is to be inserted and the slit portion, wherein after the through-bolt is inserted in the hanger portions and the boss portion in the state in which the axial position of the through-bolt relative to the boss portion is adjusted, the width of the slit portion is narrowed by fastening the fastening bolt, to reduce the diameter of the insertion-hole, thereby clamping the enlarged diameter head of the through-bolt in one hanger portion. As a result, the engine can be integrated with the body frame so as to make the engine effectively function as a member for reinforcing the body frame irrespective of the accuracy of the width of the boss portion along the axial line of the through-bolt and the accuracy of the gap between both the hanger portions. Furthermore, since the hanger portion having the slit portion is disposed on the side opposed to the side on which the chain transmission means is disposed with respect to the vehicular center line, it is possible to avoid a relatively large load being applied to the slit portion resulting from the disposition of the chain transmission means, and hence to prevent the supporting strength of the engine from being affected by the disposition of the chain transmission means.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.